It's basically distortion, like when tape overloads. People use it to warm things up a bit, put an edge on a sound to make it define and to emulate the sound of tape.

so if i am trying to keep the songs drums very punchy this would essentially be taking that away ?

Try it and see what it does for yourself. That's the best advice I can offer. If you hate it, shut it off .

thanks .... on another note do you know a good mastering guy ?

I might know one... :wink:

By the way - When you say "soft saturation" is there a particular piece of gear you're referring to?

yeah, tc electronic's eq soft sat .....